How can the address bar have "unwanted" sites on it when no one has used it but me?
You have a setting on your browser. It is currently set for: "Autocomplete entries". Turn it off.
Virus. Time for a scan.
You should check out your computer settings to ensure that there are no unwanted entries. Since you are the only one who has used it, you should also have an antivirus installed just in case that is the problem.